1. Field of the Invention
The present invention relates to a parallel-to-parallel converter used in a serial communication system for optical communications.
2. Description of the Related Art
In the field of serial communications such as optical communications, encoding techniques such as adding redundant bits to each signal for preventing consecutive high levels and low levels from taking place and keeping the ratio of high levels to low-levels constant are generally used. With a popular encoding technique called 8B10B, 8-bit data are transformed into 10-bit data before they are transmitted. On the receiving side, the received 10-bit data are transformed back into 8-bit data before they are decoded.
In a prior art serial communication system, a transmitter is formed by an 8B10B encoder and a 10 bit-to-1 bit (10-to-1) multiplexer, and a receiver is formed by a 1 bit-to-10 bit (1-to-10) demultiplexer and a 10B8B decoder. This will be explained later in detail.
In the prior art system, the transformation of a parallel signal into a serial signal and vice versa is carried out on the basis of a unit of 10 bits. Thus, the 10-to-1 multiplexer and the 1-to-10 demultiplexer are indispensable for converting the parallel signal into the serial signal and vice versa.
On the other hand, a tree-type multiplexer (or demultiplexer) adapted to a high speed parallel-to-serial (or serial-to-parallel) conversion by means of 2-to-1 multiplexers (or 1-to-2 demultiplexers) are known.
However, it is impossible to apply the high speed tree-type multiplexer or demultiplexer to the prior art serial communication system, because each circuit element is based on a 2-input and 1-output or 1-input and 2-output arrangement.